Screw and method of attachment to a substrate

Abstract

A method of implanting a threaded tapered screw into a substrate having a hardness less than the hardness of the screw comprises: (a) drilling a pilot hole with a drill having substantially the same taper as the taper of the tapered screw, so as to provide a pilot hole having no threads therein; (b) inserting the tapered screw into the pilot hole (preferably by merely dropping the screw into the pilot hole); and then (c) further advancing the tapered threaded screw into the pilot hole. The method requires only a minimal amount of strength to insert the screw into the hole, is preferably used to secure a bioabsorbable screw within bone, is very quickly and efficiently done without any extra step of tapping or cutting threads within the hole, invades or disrupts the bone structure only minimally, and requires no screw-holding forceps for stabilizing the screw. The tapered threaded bioabsorbable screw is self-centering and self-aligning and is itself a novel tapered screw especially suitable for use in orthopedics for implantation into bone. The screw has a taper and preferably has threads having rounded crests, has a slot for ease of insertion, has a single thread pitch, and is bioabsorbable.

I claim: 
     
       1. A method of securing a tapered threaded screw having threads with rounded crests for compressing a substrate and having a taper angle α and being formed from a material having a first hardness H 1  within a substrate having a second hardness H 2  which is less than said first hardness H 1  by use of a very low insertion force, said method comprising: (a) drilling a pilot hole within said substrate by use of a tapered drill having a taper angle substantially equal to said angle α of said tapered screw, so as to form a tapered unthreaded pilot hole;   (b) then inserting said tapered threaded screw into said tapered unthreaded pilot hole so that said threads of said screw only minimally contact said pilot hole so as to provide maximum congruence between said pilot hole and said screw; and then   (c) turning said screw through only a very small angle β so that said screw advances into said substrate and said threads compress and deform said substrate at places where said threads contact said substrate, thereby locking said screw within said substrate.   
     
     
       2. A method according to claim 1, wherein said method includes no step of cutting of threads by use of a tapper or by use of a self-tapping screw. 
     
     
       3. A method according to claim 2, wherein said screw is made of a bioabsorbable material. 
     
     
       4. A method according to claim 3, wherein said threads of said tapered screw have rounded crests, as opposed to having crests which are sharp cutting edges and wherein 2 times said taper angle α is within the range from about 1° to about 45°. 
     
     
       5. A method according to claim 4 wherein said tapered screw is inserted by being merely dropped into said pilot hole and wherein two times said angle α is within the range from about 5° to about 15°. 
     
     
       6. A tapered screw having a taper angle α which is within the range from about 1 to about 45 degrees, having threads which have rounded crests, as opposed to having crests which are sharp cutting edges, having a single thread pitch, and having a slot for insertion of said screw. 
     
     
       7. A tapered screw according to claim 6, wherein said screw is bioabsorbable and is part of a suture anchor and, wherein 2α is within the range from about 5° to about 15°. 
     
     
       8. A method of securing a screw made of a screw material which has a low torsional strength (as compared with the torsional strength of metal) into a substrate material having a yield strength (or ultimate strength) which is higher than the yield strength of said screw material, without tapping said substrate material, said screw having threads with rounded crests for compressing a substrate, said method comprising: (a) drilling a hole within said substrate by use of a tapered drill having a taper angle equal to said angle α, so as to form a tapered unthreaded pilot hole;   (b) inserting said tapered threaded screw into said tapered unthreaded pilot hole so that said threads of said screw only minimally contact said pilot hole, so as to provide maximum congruence between said pilot hole and said screw; and   (c) turning said screw through only a very small angle β so that said screw advances into said substrate material and said threads compress and deform said substrate material at places where said threads contact said substrate, thereby locking said screw within said substrate material.   
     
     
       9. A method according to claim 8, wherein said screw material is bioabsorbable. 
     
     
       10. A method of repairing bone fragments by use of a self-centering and self-aligning screw, said method comprising securing a screw made of a screw material which has a low torsional strength as compared with the torsional strength of metal into a substrate material having a yield strength (or ultimate strength) which is higher than the yield strength of said screw material, without tapping said substrate material, said screw having threads with rounded crests for compressing a substrate, said method comprising: (a) drilling a hole within said substrate material by use of a tapered drill having a taper angle equal to said angle α, so as to form a tapered unthreaded pilot hole;   (b) inserting said tapered threaded screw into said tapered unthreaded pilot hole so that said threads of said screw only minimally contact said pilot hole, so as to provide maximum congruence between said pilot hole and said screw; and   (c) turning said screw through only a very small angle β so that said screw advances into said substrate material and said threads compress and deform said substrate material at places where said threads contact said substrate material, thereby locking said screw within said substrate material.   
     
     
       11. A method of inserting and locking a bioabsorbable screw having a low torsional strength into a substrate material having a yield strength which is higher than the yield strength of said screw material by using only a minimal angle β of rotation of the screw, said screw having threads with rounded crests for compressing a substrate, said method comprising: (a) drilling a hole within said substrate material by use of a tapered drill having a taper angle equal to said angle α, so as to form a tapered unthreaded pilot hole;   (b) inserting said tapered threaded screw into said tapered unthreaded pilot hole so that said threads of said screw only minimally contact said pilot hole, so as to provide maximum congruence between said pilot hole and said screw; and   (c) turning said screw through only a very small angle β so that said screw advances into said substrate material and said threads compress and deform said substrate material at places where said threads contact said substrate material, thereby locking said screw within said substrate material.   
     
     
       12. A method of using a plastic, bioabsorbable, tapered screw having a taper angle α and a single thread pitch such that said screw is very quickly and very easily insertable and then very quickly and very securely lockable into place within a bone, said screw having threads with rounded crests for compressing a substrate, said method comprising: (a) drilling an unthreaded tapered hole with a tapered drill within said bone, said unthreaded tapered hole being tapered with a single taper at said taper angle α (of said tapered screw); and   (b) inserting said tapered screw within said unthreaded tapered hole such that substantially all threads of said screw contact said unthreaded tapered hole and turning said screw through an angle of at most 720°, thus fully seating and locking said screw, with substantially all threads of said screw pushing into and deforming said bone, rather than cutting said bone, and with said threads being under compression, rather than under torsion.   
     
     
       13. A method according to claim 12, wherein said angle α is between about 1° and about 45°. 
     
     
       14. A method according to claim 13, wherein said screw is a part of a suture anchor. 
     
     
       15. A method according to claim 14, wherein said screw is an interference screw (which can hold additional material in place) or a lag screw. 
     
     
       16. A method according to claim 12, wherein said tapered screw has a slot and wherein said tapered screw is inserted by placing an insertion device within said slot and then turning the insertion device.